These of course include the ubiquitous well-known Lead-Acid battery, and we all know something of the heavy lump of something-or-other that sits under the hood of our cars. Has been the same materials for over 100 years, and hasn't changed much in appearance in the last 50 years. We are talking *large* batteries here, as opposed to the little guys you pop in your torch when it goes flat.

Under the hood (so to speak) of the high-tech versions of these large lead-acid batteries, a whole lot of improvements in materials and construction has quietly gone on to make these the best batteries (so far) for just about any heavy-duty use you care to mention. There are so many types of construction to suit specific purposes, that some would be almost unrecognisable at first glance compared to the 'humble' battery in your car.Suffice to say, for the last 12 years we have been installing the same model high-tech lead-acid battery for completely off-grid systems - and once you get used to the ebb and flow of daylight-sourced power - people love 'em!! Totally reliable, safe, inert and needing no maintenance itself (other than the usual monitoring of your power usage daily in winter).

It works. It's the best bang for your buck so far.Of course, there have always been specialised competing technologies with their own quirks, foibles and cost-benefit scenarios, but lead-acid has out-competed them on pure market-driven economics.

Next, enter Lithium technology:

In nine words: "A much smaller package/weight per usable capacity battery." Does it have quirks and foibles - yes, but by and large they are controllable. There have been some 'incidents' such as overheating and combusting (ie fire), but it appears they have been restricted to "leading edge" models. The idea being that the very first of an entirely new model may reveal a shortcoming specifically due to is configuration. Generally, this is recalled, and update models (possibly even completely re-designed) are issued with controls in place to prevent any fault repetition. This has been the way of numerous streams of new technology.

Remember, Lithium batteries have been around commercially for over a decade or two in large numbers - typically things like tiny backup batteries for computer equipment, etc, and of course slightly larger main-power battery packs for portable computers. Each new model of Lithium tends to be an improvement over previous models, even if just for one attribute. For example, Lithium batteries have not been particularly widespread in *large* models, suitable for electric vehicles, telephone exchanges, and of course solar power systems.

But that has now changed: there are a number of manufacturers supplying into the Australian market, each one vying for market-share. Whilst Tesla Corp gained huge publicity with the announcement of their Lithium Battery, it so far remains as 'just another' Lithium battery system, albeit with the tantalising hope of runaway *low* pricing, which has yet to materialise!In the meantime, we here at EcoSouth have been getting our collective heads around the different offerings to be sure that we can offer value and reliability to our customers. The one *BIG* thing we believe we are seeing, so far, is that appears to be really easy to get caught-out with something either over-priced, or under-performing, or both. You could even purchase something over-sized without realising it - your vendor may not even realise it! This brings us to the *WHAT* question.

What do you want your battery system to do?Well, it's easy to work out it's got something to do with storing some power, and using it later. So how is that going to benefit you?It's all to do with a form of "power trading" - ideally you want to "buy low" and "sell high". Unfortunately, the price of exported power that you sell back to the grid is low; and the price you buy (import) power for, is high. A battery system allows a "preventative arbitrage" - let me explain. Whenever you are about to buy from the grid, it would be nice to draw from the battery instead - this *prevents* paying the high import price; but it also means that you forego the small amount you would have received had that same bit of power been exported.

So your net gain is = price of export kWh minus price of import kWh

This process can be applied by:

a) Load-Shifting Using solar to charge a battery during daylight, then discharging it into the premises in the evening. b) Peak-Shaving (or Peak Levelling) Using solar to charge a battery during daylight, but also discharging it into the premises the moment that the premise's power usage exceeds what solar is produced. In this way, momentary import is prevented during daylight hours.

With either process, once the battery has exhausted its permitted pre-designated amount of power, it must switch to being idle and do nothing until spare solar power is next available to be used to charge the battery. When the battery is idle, your premises use power in the same way it would before you had a battery system installed. Even when some solar is produced first thing in the morning the battery will not be charged as your premises will use it to reduce import power instead.

Once solar production exceeds imported power, then the battery will start charging.The concepts of Load-shifting and Peak-shaving are simple enough, BUT an implemented system "really has to know what it is doing" to be effective. Our business has already encountered some systems being offered that will Load-shift, but not Peak-shave. Also systems that do not accurately sense and hence match what is being exported, thus becoming less efficient.

Do you want power in a power-cut?

It is not true that having a battery-system alone guarantees you will have electricity in a power-cut. Sounds odd, but it is the case. It is to so with types and configurations of technology available. Generally, it is true to say that the ability to drive electrical appliances in a power-cut adds an additional cost. Similarly, achieving just load-shifting and peak-shaving can be very cost-effective.

Now, *some* battery-inverter systems may well enter the market that are not up to driving appliances by themselves! Meaning, that during a power-cut, appliance loading may be such that it will cause said inverter to fail. This is the reason why serious off-grid power systems typically use only very few brands - as they are the only ones that don't blow-up!! We know - we've even seen reputable brands blow-up in extreme cases!

So my prediction is for at least some inverter failures associated with power-cuts - unless the correct inverter set-up is selected in the first place.

What affects the purchase-price (investment cost) of battery systems?

Usable capacity - how many kWh can you store or load-shift?

How much power can you pass at once? Ie, the inverter size. A smaller inverter will pass less power, so it will take longer to load-shift of an evening, and in some cases may not shift all the power needed!

Battery lifetime - batteries are all rated for different lifetimes! This is where sellers can play fast and loose, offering a large power-shift, but very short life. An equivalent better-quality system may have the same power-shift capability, but longer life, and is more expensive initially. But is at equivalent unit-cost? ie it could be false economy to buy the cheaper system, as it will need replacing sooner - its true cost is found by extrapolating aginst the same lifetime as the more expensive system.

Warranty - how good is the installer and manufacturer their offer of the warranty? Will they help with questions, diagnosis etc? If our experience is anything to go by, the majority of suppliers aren't really interested, or resourced to help once a system is installed and paid for. We practice what we preach and provide lifetime advice and warranty help for our customers.

If this is starting to sound complex - I agree! But don't worry, we'd be more than happy to discuss this with you when you are considering a system here in Adelaide. The sizing and matching of components is *everything*, as far as economics go!

We pride ourselves on the system design and matching of the systems we offer. For a simple measurement on your part, we can advise a choice of one or more systems that will achieve cost-effective protection against rising power-bills. If you are in Adelaide, please email or call us now for a no-obligation chat and quote.

Chris Hart has been employed in the field of IT majoring in hardware and power issues for over 20 years, followed by 15 years designing and supplying solar battery systems for domestic and commercial markets. He has qualifications in electronic engineering and management.